Method for manufacturing steel wire material for reinforcing optical fiber

ABSTRACT

A method for manufacturing a steel wire material for reinforcing an optical fiber is proposed. In this method, a steel wire is firstly subjected to a chemical conversion treatment. The wire is then drawn with a reduction of area of 30% or more. As a result, a coating capable of effectively restraining the production of hydrogen is formed on the surface of the wire.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a steel wirematerial for reinforcing an optical fiber, the material having on thesurface thereof a coating capable of effectively preventing theproduction of hydrogen.

As a reinforcing material for an optical fiber, steel wire materialssuch as steel wire or strand and organic high-molecular fibers are used.Among them, since steel wire materials are inexpensive and have a highstrength and high rigidity, they are widely used.

But with the steel wire material, because its resistance to corrosion isgenerally poor, if moisture infiltrates into the optical fiber,corrosion will progress and cause the breakage of wire. Also, it ispossible that hydrogen gas is produced as a result of reaction betweenthe steel wire itself and moisture. The hydrogen gas might infiltrateinto the optical fiber, thus lowering its light transmission efficiency.Such a problem is peculiar to a steel wire for reinforcing an opticalfiber.

It is believed that there is a certain correlation between the corrosionresistance of the steel wire and the amount of hydrogen produced. Thusvarious methods have been proposed to increase the corrosion resistanceof steel wire materials used to reinforce an optical fiber.

One method is to plate a steel wire material with zinc or copper. But,because zinc plating is formed by attaching zinc having a low corrosionpotential with respect to steel to preferentially corrode the zinc andthus protect the steel against corrosion, hydrogen gas might be producedif the zinc and moisture react with each other as shown by the followingformula.

    Z.sub.n +2H.sub.2 =Z.sub.n (OH).sub.2 +H.sub.2

This will cause a reduction in the light transmission efficiency of theoptical fiber. Thus, this method is effective in protecting the steelagainst corrosion but not in preventing the production of hydrogen atall.

On the other hand, copper plating is formed by attaching to a surfacecopper having a high corrosion potential with respect to steel. In thismethod, if there is a defect in the plating surface such as a pin hole,the steel will begin to corrode from this point. In order to assure ahigh corrosion resistance, it is necessary to increase the thickness ofthe plating. But thickening the plating will result in an increase inthe plating time, thus lowering the productivity and increasing thecost.

Also it was proposed to coat a steel wire with aluminum, titanium or analloy thereof to protect the steel wire against corrosion. But with thismethod, too, the production cost tends to be rather high.

Further, it was proposed to cover a steel wire with a film of organicresin to protect the steel wire against corrosion. But in addition tothe fact that organic resins are expensive, some of them producehydrogen themselves and some allow hydrogen to pass therethrough easily.Further, in order to prevent the formation of pin holes, it is necessaryto increase the thickness of the coating. This will further increase theproduction cost.

Thus none of the conventional anti-corrosion methods was capable ofsufficiently restraining the production of hydrogen from a steel wirematerial used as a material for reinforcing an optical fiber.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing at low cost a steel wire material for reinforcing anoptical fiber, the material being provided with a coating having anexcellent corrosion resistance and less likely to produce hydrogen whilein use.

In accordance with the present invention, there is provided a method formanufacturing a steel wire material for reinforcing an optical fiber,the method comprising the steps of subjecting a steel wire to a chemicalconversion treatment to form a coating at the rate of 10 grams persquare meter or more, and drawing the wire with a reduction of area of30% or more.

In the chemical conversion treatment, a steel material is immersed in aphosphate solution or the like to form or coat a water-insolublecompound on the surface of the steel material.

Before being drawn, a steel wire is subjected to the chemical conversiontreatment to form a chemical conversion coating thereon with an amountof 10 grams per square meter or more. Then the wire is drawn with areduction of area of 30 % or more. When the wire is drawn, the chemicalconversion coating formed on the wire is pressed against the surface ofthe steel wire while keeping its high density.

The amount of the chemical conversion coating formed on the element wireshould be 10 grams per square meter or more. If it is less than 10grams, it will be impossible to sufficiently cover the steel wire andthus to effectively restrain the production of hydrogen from the steelwire.

Since the chemical conversion coating formed on the surface of the steelwire is insoluble in water and stable, the steel wire will not reactwith water at its surface. Thus the steel wire is restrained fromproducing hydrogen.

The steel wire material according to the present invention isinexpensive and is less likely to react with water and thus produceslittle hydrogen compared with a prior art zinc-plated or copper-platedwire used as a steel wire material for reinforcing an optical fiber.

Other features and objects of the present invention will become apparentfrom the following description taken with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the amount ofhydrogen produced and the testing time in the hydrogen producing test inwhich various steel wire materials were reacted with moisture;

FIG. 2 is a graph showing the relationship between the reduction of areaand the amount of hydrogen produced in 100 hours after the hydrogenproducing test has begun in which steel wires treated with zincphosphate and drawn with different area reduction rates were reactedwith water; and

FIG. 3 is a graph showing the relationship between the amount ofmanganese phosphate formed on the steel wire and the amount of hydrogenproduced in 100 hours after the hydrogen producing test has begun inwhich the steel wire treated with manganese phosphate was reacted withwater.

FIRST EXAMPLE

Steel wires having their surface coated with zinc phosphate underdifferent conditions, a zinc-plated steel wire and a steel wire thicklyplated with copper were compared with one another in the amount ofhydrogen produced.

Table 1 shows the surface conditions of the specimens, which are elementwires 1.8 mm in diameter.

These wires were drawn until their diameters are reduced to 0.6 mm(reduction of area: 89%)

The thus drawn specimens shown in Table 1 were plated in a sealed vesseltogether with water, the amount of which is equal to 0.5 percent of theinternal volume of the vessel and kept in a constant temperature bath at80° C. Then the amounts of hydrogen produced by the reaction betweenmoisture and metal were measured by gas chromatography. The results areshown in FIG. 1.

The results show that specimens according to the present inventionproduce little hydrogen compared with the other specimens.

SECOND EXAMPLE

Among the specimens shown in Table 1, the steel wires treated with zincphosphate B, which were in the form of element wires 1.8 mm in diameter,were drawn to different diameters and put to the same hydrogen producingtest as in the first Example.

The amount of hydrogen produced from each of the steel wires wasmeasured by gas chromatography. The results are shown in FIG. 2.

The results show that if the reduction of area is less than 30%, it isdifficult to effectively restrain the production of hydrogen.

THIRD EXAMPLE

The amounts of hydrogen produced were checked for the steel wires coatedwith manganese phosphate.

Table 2 shows the amounts of manganese phosphate formed on thespecimens, that is, the element wires 1.8 mm in diameter.

The specimens were drawn until their diameters were reduced to 0.8 mm(reduction of area: 75%). Then they were put to the same hydrogenproducing test as in the first Example.

The amounts of hydrogen produced in 100 hours were measured by gaschromatography. The results are shown in FIG. 3. The results show thatthe steel wires treated with manganese phosphate with an amount of 10grams per square meter or more produced little hydrogen.

                  TABLE 1                                                         ______________________________________                                        Specimen          Surface condition                                           ______________________________________                                        Steel wire treated with                                                                         Zinc phosphate coating                                      zinc phosphate (A)                                                                              formed with                                                                   amount of 4-6 gr/m.sup.2                                    Present Invention                                                             Steel wire treated with                                                                         Zinc phosphate coating                                      zinc phosphate (B)                                                                              formed with                                                                   amount of 13-15 gr/cm.sup.2                                 Steel wire treated with                                                                         Zinc phosphate coating                                      zinc phosphate (C)                                                                              formed with                                                                   amount of 24-26 gr/cm.sup.2                                 Steel wire treated with                                                                         Zinc phosphate coating                                      zinc phosphate (D)                                                                              formed with                                                                   amount of 38-41 gr/cm.sup.2                                 Zinc plated       Plating with molten zinc                                    steel wire        formed zinc film                                                              about 30-40 microns thick                                                     with 150-200 gr/m.sup.2                                     Copper plated     Plating with copper                                         steel wire        pirrolinate and copper                                                        sulfate formed copper                                                         film about 1.5-2 microns                                                      thick with 13-15 gr/m.sup.2                                 Thickly copper    Plating with copper                                         plated steel wire pirrolinate and copper                                                        sulfate formed copper                                                         film about 6-8 microns                                                        thick with 50-60 gr/m.sup.2                                 ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Specimens       Amount coated                                                 ______________________________________                                        Steel wire treated                                                                             5 gr/m.sup.2                                                 with manganese                                                                phosphate (E)                                                                 Steel with treated                                                                            14 gr/m.sup.2                                                 with manganese                                                                phosphate (F)                                                                 Steel with treated                                                                            26 gr/m.sup.2                                                 with manganese                                                                phosphate (G)                                                                 ______________________________________                                    

What is claimed is:
 1. The method of manufacturing an optical fiberreinforced with a steel wire which comprises;immersing a steel wire in asolution of phosphate chemical conversion coating compound; depositingat least 13 grams per square meter of said chemical conversion coatingon said steel wire; drawing said coated steel wire to reduce its area atleast 30% to compact said coating thereon, whereby forming a coatedsteel wire which is substantially unreactive with water to evolvehydrogen; and compositing said coated steel wire with an optical fiberin a reinforcing relationship.
 2. The method as claimed in claim 1wherein said chemical conversion coating is magnesium phosphate.
 3. Themethod as claimed in claim 1 wherein said chemical conversion coating iszinc phosphate.
 4. A reinforced optical fiber comprising an opticalfiber and a steel wire in reinforcing relationship thereto, wherein saidsteel wire has disposed thereon, under said optical fiber, a phosphatechemical conversion coating which was applied by coating a steel wirewith at least 13 grams power square meter of said chemical conversioncoating and then drawing said coated steel wire down an amount such asto reduce its area at least 30%.
 5. A reinforced optical fiber asclaimed in claim 4 wherein said chemical conversion coating is magnesiumphosphate.
 6. A reinforced optical fiber as claimed in claim 4 whereinsaid chemical conversion coating is zinc phosphate.